The present invention relates to the sealing of plastic lids or closures to plastic containers and, more particularly, to the spin welding of lids and containers.
The process of spin welding is one in which the friction between relatively rotating lids and containers such as bowls and cups causes the synthetic resin at abutting surfaces to melt and bond the two surfaces upon cooling. Generally, many spin welding processes have involved spinning the lid or cover at a relatively high speed and then bringing it into contact with the container which produces the melting friction as the lid rotation is slowed and then stops. Exemplary of such a process is U.S. Pat. No. 3,297,504 to Brown et al.
The industry has been seeking ever shorter spin welding cycles to expedite the filling and sealing process, while obtaining a reliable weld over the entire circumference to ensure a good seal.
Hofuis et al U.S. Pat. No. 5,772,103 describes an alternate process in which the lid and container are first brought into contact under vertical load and then rotational force is applied for a preset small number of rotations to effect the desired fusion.
In any spin welding process, there is a problem in dealing with variables such as variations in surface characteristics and configuration, contamination of the abutting surfaces by the contents of the container during filling, etc.
Accordingly, it is an object of the present invention to provide a novel method of spin welding lids and containers which will accommodate surface variations and produce well sealed containers.
It is also an object to provide such a method which may be practiced easily and rapidly in high speed filling lines.
Another object is to provide novel apparatus for spin welding lids and containers which accommodates surface variations and produces well sealed containers.